^^^It didn't smell like fuel, but you could be right. Now that I've had a decent night's sleep, I'm thinking straight again- I can't see how every single plug and cylinder could be oil fouled. I don't think it's the O2 sensor, more like the O2 sensor is getting damaged each time I replace it because of something else. All the engine sensors and senders have now been replaced, maybe it's the fuel pressure regulator?